1. Field of the Invention
Counterbalancing mechanisms with particular reference to a spring counterbalance for an adjustable instrument supporting arm.
2. Discussion of the Prior Art
Ophthalmic instrument supporting arms and the like which are raised and lowered on instrument stands to various working heights are commonly spring balanced in an intermediate position of adjustment. As the arm and instrument or other load carried thereby is raised or lowered, the springs are caused to extend or retract rendering the arm unbalanced and in need of friction breaking or other such means to maintain desired positions of arm adjustment above or below the intermediate or other preselected position of balance. Thus, manipulation of such an instrument supporting arm over the full excursion of its adjustment requires variable forces, the greatest usually being adjacent points where frictional breaking is maximum, i.e. at points furthest from actual balancing. This "feel" of unevenness of arm operation can be disconcerting to the practitioner desiring to avoid jerky or otherwise uneven arm adjustments particularly when aligning an ophthalmic instrument with the face or eyes of a patient.
Attempts to avoid the drawbacks of conventional spring biasing of instrument stand arms and the like have included the use of balancing weights and pulleys. While such means may offer relatively uniform counterbalancing at most positions of arm adjustment, their large space requirements and general ungainliness usually outweigh advantages.
An object of the present invention is to accomplish substantially constant counterbalancing of a spring biased instrument supporting arm over its entire excursion of adjustment.
More particularly, the objective is to provide spring counterbalancing of an instrument stand arm or the like with automatic compensation for inherent variations of spring extension forces.
Another object is to provide a mechanism for adjustable arm counterbalancing which is adaptable to light, intermediate or heavy load carrying apparatus.
Still another object is to accomplish the above with maximum mechanical simplicity and compactness.
Other objects and advantages of the invention will become apparent from the following description.